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What Is Java?
• According to Sun in a white paper:
Java: A simple, object-oriented, network-savvy,
interpreted, robust, secure, architectureneutral, portable, high-performance,
multithreaded, dynamic language
Java is Object-Oriented
• There are over 100 programming languages
• Popular languages: FORTRAN, COBOL, Visual BASIC,
Pascal, Ada, C, C++
• Each language was designed for a specific purpose.
• All except for C++ are known as procedural
programming languages.
Java is Distributed
• Distributed computing involves several
computers working together on a network.
• Networking capability is inherently integrated
into Java so writing network programs is like
sending and receiving data to and from a file.
Java is simple
• Java is partially modeled on C++ but greatly
simplified and improved.
Examples: Pointers & multiple inheritance often
make programming complicated. Java replaces the
multiple inheritance in C++ with a simple language
construct and eliminates pointers.
Java uses automatic memory allocation and garbage
Object Oriented
• In a procedural language, a problem is solved using
the paradigm of procedures.
• OOP models the real world in terms of objects.
• Programming in Java is centered on creating objects,
manipulating objects, and making objects work
Java is compiled and interpreted
• The Java platform has a compiler that translates Java
source into a form called bytecodes
• Bytecode is an architecturally neutral representation
of code written in the Java programming language. It
is machine-independent and can run on any machine
that has a Java interpreter.
• The bytecode rather than Java source code, is
interpreted when you run a Java program.
Java is robust
• Robust means reliable.
• Java has eliminated certain error-prone programming
constructs found in other languages.
• It doesn’t support pointers, for example, thereby eliminating
the possibility of overwriting memory and corrupting data.
• Java has a runtime exception-handling feature to provide
programming support for robustness.
• The programmer must write the code to deal with exceptions.
Java is Secure
• This is essential since it lends itself to programming
for the Internet & WWW
• If you download a Java applet and run it on your
computer, it will not damage your system because
Java implements several security mechanisms.
• Java security is based on the premise that nothing
should be trusted.
Java is Portable
• Java programs can be run on any platform
without being recompiled, making them very
• There are no platform-specific features in Java
(size of an int).
Java is architecture neutral
• The language allows for no implementationdefined features.
Example: the size of a variable int
• All Java programs must be compiled into
bytecodes before the JVM can run them.
Java’s Performance
• Surprisingly good compared to other
interpreted languages
• The new Java Development Kit uses the
technology known as just-in-time compilation.
– JVM searches for hot spots (parts of the bytecode
executed frequently)
– JIT compiler translates the hot spots into
underlying machine language
Java is multithreaded
• This is the capability for a program to perform several tasks
simultaneously within a program
Example: Download a video file while playing the video
• Used in graphical user interfaces (listen to an audio
recording while surfing a Web page)
• Used in network programming (a server can serve multiple
clients at the same time).
• Classes are provided from the base language package to
create and manage threads
History of Java
• Story starts in early 1990s
• Sun Microsystems was working on consumer electronics
with the objective of keeping price down.
• Software for consumer electronics is developed on the
cheapest chips available
• If a different chip set becomes cheaper, the developers must
switch to that chip.
• Sun’s goal -- develop software that was portable so that it
could be switched quickly to new hardware.
History continued
• The language was first called Oak (after an oak tree
outside Goslings window). However, there was
already a language named Oak so the team named
the language Java (in recognition of the role that
caffeine plays in software development.
• Sun formally announced Java at a major conference
in 1995.
Java is Dynamic
• Java was designed to adapt to an evolving
• You can freely add new methods to a class without
affecting its clients.
Example: In the Circle class, you can add a new data property
to indicate the color of the circle or a new method to obtain
the circumference of the circle. The original client program
that uses the circle class remains the same.
• Also, at runtime Java loads classes as they are
History Continued
• The Green project started in 1991 and the goal was to create
an experimental, hand-held computer (PDA) called the *7,
intended for controlling home appliances.
• James Gosling was the technical leader of the project.
• A language was developed for the *7 project which was
called Oak.
• The *7 never became a product but due to the explosion in
popularity of the WWW, the team saw that the language
could be very useful.
History Continued
• Major byproduct of the Green project was
• Duke was the ebodiment of the “agent” in the
Green user interface.
• Became the Java mascot.